Artificial leaves that produce hydrogen could soon be even better at their job, thanks to a new study that examined the effects of pressure on the chemical processes they carry out. It all comes down to bubbles.
When it comes to certain processes, it’s hard to beat nature. Take photosynthesis, for example. Trees can absorb carbon dioxide from the air through their leaves, combine it with water, and extract the energy they need to live, while also sending back a healthy dose of oxygen to the rest of the planet.
So instead of trying to do better than a leaf, scientists have spent years trying to mimic it and apply its principles in unique ways. While we’ve seen artificial leaves that can produce everything from synthetic gas to pharmaceutical drugs, one of the most promising uses for the little pieces of technology is to release hydrogen from air and water. This happens in natural photosynthesis, as plants split hydrogen and oxygen atoms from water molecules.
Today’s hydrogen-producing artificial leaves (known as photoelectrochemical cells (PECs)) use light-activated electrodes to create a current that splits water into hydrogen and oxygen. The best of these have an energy conversion ratio of 19%, a measure of how much net power is produced by a system. For comparison, the best solar panels currently in operation have an energy conversion ratio of about 24%.
One of the problems with pushing PECs beyond this range is that during operation, bubbles start to form in the electrolyte solution that the electrodes are working in. These bubbles can prevent the solution from contacting the electrodes and can also affect the system's ability to absorb light.
Thinking they could solve the bubble problem, researchers at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) in Germany tested the idea of applying more atmospheric pressure to the inner workings of PECs. They found that if the operating pressure was increased to 8 bar, they could keep the bubbles under control enough to halve the system’s total energy loss, which could lead to an energy conversion rate 5-10% higher than current gold-standard systems.
“At this pressure, optical scattering losses can be almost completely avoided,” said Feng Liang, first author of the study. “We also saw a significant reduction in product migration, especially the transfer of oxygen to the counter electrode.”
Liang and colleagues published their findings in the journal Nature Communications.
Source: HZB